The present invention is directed to thermally transferable compositions for use in imaging applications. The invention also relates to thermal transfer articles, to graphic articles comprising a graphic image formed using the thermally transferable compositions, and to methods of making and using such thermally transferable compositions.
Graphic articles, such as advertisements, traffic signs, banners, license plates, retail signs, on-vehicle graphics, etc. are widely used. Depending upon the application such articles are often subjected to demanding environmental conditions, including exposure to extreme temperature fluctuations, exposure to precipitation, sunlight, and physical wear from contact with people or objects, chemical attack by cleaning fluids or solvents, and other chemical agents in the environment. Graphic articles used in exterior applications face particularly harsh weathering conditions, and must be produced such that they are able to withstand such conditions.
Graphic articles can be formed by various methods. These methods include, for example, screen-printing methods, lithographic printing methods, and adhesive sheet transfer methods. One specific method of forming graphic articles is thermal transfer, which transfers a color layer from a first substrate or carrier film, usually a plastic film, to a second substrate or target surface. Thermal transfer methods form the graphic image by selectively transferring only portions of the color layer from the first substrate onto the second substrate. One advantage of thermal transfer methods is that they allow the color layer to be made as a uniform sheet without a latent image, and the graphic pattern is defined by controlling the application process. This allows a limited number of carrier films to be used to produce a great variety of customized graphic articles.
During the thermal transfer process it is desirable to have the thermally transferable composition readily transfer from the carrier to the target surface. This can be facilitated, for example, by using a thermally transferable composition that softens at low temperatures so that it readily transfers upon application of heat. Unfortunately, thermally transferable compositions that melt or soften at low temperatures can also be less durable when exposed to high temperatures during use. It is also desirable that the thermally transferable composition transfers cleanly to produce sharp edges along its perimeter. This allows creation of more precise transfers with greater sharpness and detail. It is desirable that the thermally transferred composition has good durability, and be able to withstand temperature fluctuations and other related environmental exposure. In particular, it is desirable that the cured composition has good durability without the need to perform excessive additional production steps or use additional materials, such as over-laminating with a protective layer.
Although graphic articles having images formed by thermal transfer normally provide satisfactory print quality, legibility, and adhesion, a need remains for improved thermally transferable compositions and articles.
The present invention is directed to thermally transferable compositions and articles, and methods of using the compositions and articles. The compositions permit easy, precise transfer of color layers to various substrates; and are photocurable to produce a strong, durable, weatherable image.
The photocurable, thermally transferable compositions of the invention include a multifunctional monomer that is substantially non-liquid at room temperature, plus a thermoplastic binder. The multifunctional monomer normally contains from 15 to 60 carbon atoms, and can include a dicyclohexane compound of the general formula: 
wherein R1 and R2 comprise functional groups containing a total of at least two acrylate groups. Suitable multifunctional monomers include dicyclohexane compounds of the general formula: 
wherein at least two, and typically two to four, of R1 to R10 comprise functional groups containing acrylate groups.
The relative amounts of multifunctional monomer and binder depend upon the application, and specific applications use a composition that contains 50 percent or more by weight multifunctional monomer based upon total weight of multifunctional monomer and binder. In other implementations the composition contains from 60 to 80 percent by weight multifunctional monomer and from 20 to 40 percent by weight thermoplastic polymeric binder based upon total weight of multifunctional monomer and binder.
The invention includes thermal transfer articles containing a substrate, and a photocurable thermally transferable composition on the substrate. The photocurable thermally transferable composition contains a multifunctional monomer that is substantially non-liquid at room temperature and a binder. The substrate can be, for example, a ribbon or a sheet.
The invention is also directed to various printed articles containing a photocured coating formed from the cured composition of the invention. Specifically, the articles include one or more layers of a thermally transferable composition containing a multifunctional monomer that is substantially non-liquid at room temperature and a thermoplastic binder. The thermally transferable composition is applied to the article using heat to soften the composition. After transfer the composition is cured using actinic radiation to crosslink the monomer at its functional groups and provide a durable finished graphic article.
The invention also includes methods for forming a photocured thermally transferred image. The method includes providing a photocurable composition containing a multifunctional monomer that is substantially non-liquid at room temperature and a thermoplastic binder; heating the photocurable composition; transferring the photocurable composition to a substrate; and crosslinking the photocurable composition by exposure to actinic radiation.
Other features and advantages of the invention will be apparent from the following detailed description of the invention and the claims. The above summary of principles of the disclosure is not intended to describe each illustrated embodiment or every implementation of the present disclosure. The drawings and the detailed description that follow more particularly exemplify certain embodiments utilizing the principles disclosed herein.